Reservation channel transmission forwarding in vehicle-to-vehicle communications

ABSTRACT

The methods and systems discussed herein describe how a first wireless communication device forwards a reservation signal, which identifies one or more time-slots that have been reserved by a second wireless communication device, to avoid “merging collisions.” In some examples, the first wireless communication device determines that it should forward the reservation signal based on a determination that the first wireless communication device is located at the edge of a coverage area associated with the second wireless communication device. This determination can be based on location information associated with the second wireless communication device or whether a received power value of the reservation signal is within a pre-defined threshold range value. In other examples, the first wireless communication device transmits an updated forwarded reservation signal, which is an update of a previously forwarded reservation signal in which multiple time-slots were reserved.

CLAIM OF PRIORITY

The present application claims priority to Provisional Application No. 62/754,408, entitled “RESERVED TIME-SLOTS LIST TO AVOID TRANSMISSION COLLISIONS IN VEHICLE-TO-VEHICLE COMMUNICATIONS”, filed Nov. 1, 2018, and Provisional Application No. 62/758,770, entitled “RESERVATION CHANNEL TRANSMISSION FORWARDING IN V2V COMMUNICATIONS”, filed Nov. 12, 2018, both of which are assigned to the assignee hereof and hereby expressly incorporated by reference in their entirety.

FIELD

This invention generally relates to wireless communications and more particularly to vehicle-to-everything (V2X) communications between wireless communication devices.

BACKGROUND

A vehicle ad-hoc network (VANET) is an autonomously created wireless network of vehicles. In some VANETs, the wireless communication devices, which are located within the vehicles of the VANET, autonomously select the time-frequency resources for data transmissions to other vehicles within the VANET. However, if the number of transmitting vehicle-to-vehicle (V2V) devices is large with respect to the resources available for data transmissions, the probability of data transmission collisions is high.

SUMMARY

The methods and systems discussed herein describe how a first wireless communication device forwards a reservation signal, which identifies one or more time-slots that have been reserved by a second wireless communication device, to avoid “merging collisions.” In some examples, the first wireless communication device determines that it should forward the reservation signal based on a determination that the first wireless communication device is located at the edge of a coverage area associated with the second wireless communication device. This determination can be based on location information associated with the second wireless communication device or whether a received power value of the reservation signal is within a pre-defined threshold range value. In other examples, the first wireless communication device transmits an updated forwarded reservation signal, which is an update of a previously forwarded reservation signal in which multiple time-slots were reserved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an example of a system in which a plurality of wireless communication devices are nodes of a vehicle ad-hoc network (VANET).

FIG. 1B is a block diagram of an example of a system in which the wireless communication devices of FIG. 1A are using reservation signal forwarding to avoid data transmission collisions in the VANET.

FIG. 2A is a block diagram of an example of the base station shown in FIG. 1A.

FIG. 2B is a block diagram of an example of a wireless communication device shown in FIG. 1A.

FIG. 3 is a diagram of an example in which a reservation signal is transmitted over a first portion of a time-slot and a forwarded reservation signal is transmitted over a second portion of the time-slot.

FIG. 4 is a flowchart of an example of a method in which a first wireless communication device receives, from a second wireless communication device, a reservation signal that identifies one or more time-slots that have been reserved by the second wireless communication device for data transmissions. The first wireless communication device transmits a forwarded reservation signal that identifies the one or more time-slots that have been reserved by the second wireless communication device.

DETAILED DESCRIPTION

The examples discussed below are generally directed to vehicle-to-vehicle (V2V) communication between two or more vehicles that are part of a vehicle ad-hoc network (VANET). However, any of the following examples may be applied to vehicle-to-everything (V2X) communication, which is the passing of information from a vehicle to any entity that may affect the vehicle or that the vehicle may affect. For example, V2X is a vehicular communication system that incorporates other, more specific types of communication, including V2V, V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), V2P (vehicle-to-pedestrian), V2D (vehicle-to-device), and V2G (vehicle-to-grid). There are two types of V2X communication technology depending on the underlying technology being used: wireless local area network (WLAN)-based V2X, and cellular-based V2X (C-V2X). Some examples of V2X protocols include Long-Term Evolution (LTE) (Rel-14) V2X Mode 4 and 5G New Radio (NR) V2X Mode 2.

In order to minimize the number of data transmission collisions in a VANET, a wireless communication device interested in transmitting data transmits a reservation signal, which is also referred to herein as a reservation channel transmission, which indicates resources to be used for the data transmission at a future time. The other wireless communication devices in the VANET receive and decode this reservation signal in order to identify the resources that will be used by the transmitting wireless communication device for future data transmissions. In order to avoid collisions, the other wireless communication devices take the resources identified in the reservation signal into account when selecting transmission resources that will be used for their respective future data transmissions.

In accordance with one example of a resource selection method, a wireless communication device that is interested in transmitting data uses long-term sensing to discover which resources are already periodically being used by one or more other wireless communication devices. When an actual data packet arrives at the wireless communication device, the wireless communication device uses short-term sensing to detect, among the remaining idle resources, an idle set of resources. In general, the sensing may be based on the successful decoding of the control channel and/or the signal-to-noise measurement of the reference signals embedded within the control/data channels above a given threshold value. The wireless communication device then transmits a reservation signal to reserve resources, which were identified as being idle, for a future data transmission.

Although the sensing method allows the wireless communication devices to select the unused time-slots, it is still possible for the data transmissions to collide due to the mobility of the wireless communication devices. For example, a “merging collision” occurs when a first wireless communication device moves into a region where there is already a second wireless communication device using the same time-slot as the first wireless communication device. For example, as shown in FIG. 1B, a “merging collision” would happen when the accelerating wireless communication device 106 is about to enter the coverage area 111 of wireless communication device 110 and both wireless communication devices 106, 110 happen to be using the same time-slot, t_(m), for their respective data transmissions. The sensing method, described above, does not help avoid the “merging collision” in this scenario because wireless communication device 106 will not detect the out-of-range wireless communication device 110.

The methods and systems discussed herein describe how a first wireless communication device 108 forwards a reservation signal, which identifies one or more time-slots that have been reserved by a second wireless communication device 110, to avoid “merging collisions.” In some examples, the first wireless communication device determines that it should forward the reservation signal based on a determination that the first wireless communication device is located at the edge of a coverage area associated with the second wireless communication device. In other examples, the first wireless communication device transmits an updated forwarded reservation signal, which is an update of a previously forwarded reservation signal in which multiple time-slots were reserved.

For the examples described herein, it is assumed that the wireless communication devices are equipped with a Global Positioning System (GPS) receiver and that synchronization among the wireless communication devices is performed using the one pulse-per-second (1PPS) signal provided by the GPS receiver. Using the 1PPS signal, the wireless communication devices obtain common reference timing, synchronized with each other and become aware of the frame-boundaries. Each frame consists of a constant number of fixed duration time-slots (e.g., the duration of each frame is 100 milliseconds long where each time-slot within the frame is 0.5 ms, resulting in 200 time-slots per frame). As a result, every wireless communication device has the knowledge of the frame-number and time-slot-number.

FIG. 1A is a block diagram of an example of a system in which a plurality of wireless communication devices are nodes of a vehicle ad-hoc network (VANET). For the example of FIG. 1A, VANET 100 is located on roadway 101 and includes first wireless communication device, WCD1, 108, second wireless communication device, WCD2, 110, and third wireless communication device, WCD3, 106. In other examples, VANET 100 may have a different number of wireless communication devices than that shown in FIG. 1A.

VANET 100 is wirelessly connected to a radio access network (not shown) via an infrastructure communication node (e.g., base station 102 or a road side unit (RSU)), which provides various wireless services to one or more of the wireless communication devices that are part of VANET 100. For the example shown in FIG. 1A, VANET 100 operates in accordance with at least one revision of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication specification. In other examples, VANET 100 may operate in accordance with other communication specifications.

In the interest of clarity and brevity, only one infrastructure communication node (e.g., base station 102) is shown in FIG. 1A. However, in other examples, any suitable number of infrastructure communication nodes may be utilized by VANET 100 in order to obtain/maintain communication with the network. For the example shown in FIG. 1A, base station 102, sometimes referred to as eNodeB or eNB, communicates with wireless communication devices 106, 108, 110 via wireless communication link 104. As referenced earlier, the infrastructure communication node is a road side unit (RSU), in other examples.

For the example shown in FIG. 1A, wireless communication link 104 is shown as a broadcast downlink signal from base station 102 to wireless communication devices 106, 108, 110. Wireless communication devices 106, 108, 110 are also capable of transmitting uplink signals (not shown) to base station 102. In the example of FIG. 1A, wireless communication devices 106, 108, 110 are each integrated into a vehicle as an onboard unit (OBU). In other examples, wireless communication devices 106, 108, 110 may simply be user equipment (UE) devices that are located within a vehicle. Some examples of user equipment devices include: a mobile phone, a transceiver modem, a personal digital assistant (PDA), or a tablet, for example. Each wireless communication device 106, 108, 110 that is connected to VANET 100 is considered to be a node of VANET 100. As indicated by the arrow in FIG. 1A, the vehicles in which wireless communication devices 106, 108, 110 are located are traveling from left to right on roadway 101.

Base station 102 is connected to the network through a backhaul (not shown) in accordance with known techniques. As shown in FIG. 2A, base station 102 comprises controller 204, transmitter 206, and receiver 208, as well as other electronics, hardware, and code. Base station 102 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to base station 102 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

For the example shown in FIG. 2A, base station 102 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. In some situations, base station 102 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and/or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, base station 102 may be a portable device that is not fixed to any particular location. Accordingly, base station 102 may be a portable user device such as a UE device in some circumstances.

Controller 204 includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of base station 102. An example of a suitable controller 204 includes code running on a microprocessor or processor arrangement connected to memory. Transmitter 206 includes electronics configured to transmit wireless signals. In some situations, transmitter 206 may include multiple transmitters. Receiver 208 includes electronics configured to receive wireless signals. In some situations, receiver 208 may include multiple receivers. Receiver 208 and transmitter 206 receive and transmit signals, respectively, through antenna 210. Antenna 210 may include separate transmit and receive antennas. In some circumstances, antenna 210 may include multiple transmit and receive antennas.

Transmitter 206 and receiver 208 in the example of FIG. 2A perform radio frequency (RF) processing including modulation and demodulation. Receiver 208, therefore, may include components such as low noise amplifiers (LNAs) and filters. Transmitter 206 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station.

Transmitter 206 includes a modulator (not shown), and receiver 208 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signal 104 and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at base station 102 in accordance with one of a plurality of modulation orders.

As mentioned above, base station 102 provides (1) various wireless services to one or more wireless communication devices 106, 108, 110, and (2) network connectivity to VANET 100. Base station 102 provides these services and connectivity by transmitting downlink signal 104, via transmitter 206 and antenna 210, to wireless communication devices 106, 108, 110. In the example of FIG. 1A, the downlink signal 104 is transmitted in a System Information Block (SIB) message that is broadcast to all wireless communication devices 106, 108, 110 that are nodes of VANET 100. Although not explicitly shown in FIG. 1A, base station 102 is capable of receiving uplink signals, via antenna 210 and receiver 208, from wireless communication devices 106, 108, 110.

As shown in FIG. 2B, wireless communication device 106 comprises controller 216, transmitter 218, and receiver 214, as well as other electronics, hardware, and code. Although FIG. 2B specifically depicts the circuitry and configuration of wireless communication device 106, the same wireless communication device circuitry and configuration is utilized for wireless communication devices 108, 110 in VANET 100. Wireless communication device 106 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to wireless communication device 106 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

Controller 216 includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of a wireless communication device. An example of a suitable controller 216 includes code running on a microprocessor or processor arrangement connected to memory. Transmitter 218 includes electronics configured to transmit wireless signals. In some situations, the transmitter 218 may include multiple transmitters. Receiver 214 includes electronics configured to receive wireless signals. In some situations, receiver 214 may include multiple receivers. Receiver 214 and transmitter 218 receive and transmit signals, respectively, through antenna 212. Antenna 212 may include separate transmit and receive antennas. In some circumstances, antenna 212 may include multiple transmit and receive antennas.

Transmitter 218 and receiver 214 in the example of FIG. 2B perform radio frequency (RF) processing including modulation and demodulation. Receiver 214, therefore, may include components such as low noise amplifiers (LNAs) and filters. Transmitter 218 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the wireless communication device functions. The required components may depend on the particular functionality required by the wireless communication device.

Transmitter 218 includes a modulator (not shown), and receiver 214 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as uplink signals (not shown). The demodulator demodulates the downlink signals 104 in accordance with one of a plurality of modulation orders.

In the example shown in FIG. 1B, there is a possibility of a “merging collision” between wireless communication device 106 and wireless communication device 110. Direct communication of a reservation signal (e.g., reservation channel transmission) between wireless communication devices 106 and 110 is not possible since coverage area 107 of wireless communication device 106 cannot reach wireless communication device 110. Similarly, coverage area 111 of wireless communication device 110 cannot reach wireless communication device 106. However, coverage area 109 of wireless communication device 108 can reach both wireless communication device 106 and wireless communication device 110.

As wireless communication device 106 accelerates (e.g., from left to right, as shown by the dashed arrow) and gets closer to wireless communication device 110, there is a possibility of a “merging collision” to occur in time-slot t_(m), which is being used by both wireless communication devices 106, 110 for data transmissions. Wireless communication device 108 receives reservation signal 112 from wireless communication device 110. Reservation signal 112 identifies one or more time-slots, including time-slot t_(m), that have been reserved by wireless communication device 110 for data transmissions within VANET 100.

Wireless communication device 108 transmits (e.g., broadcasts) forwarded reservation signal 114 to other wireless communication devices in VANET 100. Forwarded reservation signal 114 identifies the one or more time-slots that have been reserved by wireless communication device 110 for data transmissions within VANET 100. Forwarded reservation signal 114 is based, at least partially, on reservation signal 112 and contains information upon which one or more additional wireless communication devices may determine whether to transmit data within the one or more time-slots identified in forwarded reservation signal 114. Wireless communication device 106 receives forwarded reservation signal 114 that was transmitted from wireless communication device 108. Since time-slot t_(m) is listed as one of the reserved time-slots being used by a neighboring wireless communication device, wireless communication device 106 refrains from transmitting data in time-slot t_(m) and starts the process of selecting an unused time-slot. As a result, the “merging collision” is avoided.

In some examples, reservation signal 112 and/or forwarded reservation signal 114 comprise one or more of the following: reservations for multiple time-slots, Global Positioning System (GPS) information, a zone identifier (zone ID), a number of time-slots reserved information, a cell identifier (cell ID), a group identifier (group ID), a frame-offset, and a subframe-offset. Reservations for multiple time-slots refers to examples in which a single reservation signal or forwarded reservation signal identifies a plurality of time-slots (e.g., time-slots T_(A), T_(B), and T_(C)) that have been reserved for data transmissions. The GPS information includes, for example, information such as a wireless communication device's geo-location, speed, heading, and zone identifier. The zone identifier (zone ID) identifies a zone in which a wireless communication device is located. A number of time-slots reserved information refers to examples in which a single reservation signal or forwarded reservation signal contains a number (e.g., 3 time-slots) that indicates how many time-slots are being reserved by that particular reservation signal or forwarded reservation signal. A cell identifier (cell ID) identifies a cell that is serving a wireless communication device. A group identifier (group ID) identifies a group to which a wireless communication device belongs. The frame-offset indicates the frame-offset being used by a wireless communication device. The subframe-offset indicates the subframe-offset being used by a wireless communication device. Inclusion of one or more of the foregoing items in reservation signal 112 and/or forwarded reservation signal 114 advantageously provides information when the wireless communication devices are served by different operators and/or by different base stations. For example, each base station could have a different frame numbering. Thus, the wireless communication devices can take information such as the cell ID and the offset into account to identify the reserved time-slots from a wireless communication device served by a different base station.

In some examples, wireless communication device 108 determines that wireless communication device 108 should forward reservation signal 112 from wireless communication device 110 as forwarded reservation signal 114. For example, if wireless communication device 108 is located near an edge of coverage area 111 associated with wireless communication device 110, then wireless communication device 108 determines that wireless communication device 108 should forward reservation signal 112 from wireless communication device 110 as forwarded reservation signal 114. In some examples, wireless communication device 108 determines that it is located near an edge of coverage area 111 associated with wireless communication device 110 by determining whether a received power value of reservation signal 112, as measured at wireless communication device 108, is within a pre-defined threshold range value. In other examples, wireless communication device 108 determines that it is located near an edge of coverage area 111 associated with wireless communication device 110 based, at least partially, on location information associated with the wireless communication device 110. In some instances, wireless communication device 108 receives the location information (e.g., GPS information and/or zone ID) associated with the wireless communication device 110 in reservation signal 112. In other instances, wireless communication device 108 could already be in communication with wireless communication device 110 such that wireless communication device 108 is already aware of the location of wireless communication device 110.

In other examples, wireless communication device 108 autonomously re-broadcasts updates to a previously forwarded reservation signal 114. For example, assume that reservation signal 112 and forwarded reservation signal 114 both identify a plurality of time-slots (e.g., T_(A), T_(B), and T_(C)) that are reserved by wireless communication device 110. After wireless communication device 110 transmits data utilizing time-slot T_(A), wireless communication device 108 will transmit an updated forwarded reservation signal that identifies one or more remaining time-slots (e.g., T_(B) and T_(C)), which were previously reserved by wireless communication device 110 for data transmissions within the VANET. Thus, in this example, the first updated forwarded reservation signal, which identifies T_(B) and T_(C), is transmitted after at least one data transmission by wireless communication device 110 that utilizes time-slot T_(A). The second updated forwarded reservation signal, which identifies T_(C), is transmitted after at least one data transmission by wireless communication device 110 that utilizes time-slot T_(B). In some examples, the number of time-slots reserved information (e.g., the number of reserved time-slots) is included in reservation signal 112 transmitted from wireless communication device 110.

Once wireless communication device 108 determines that it should forward reservation signal 112 as forwarded reservation signal 114, it is important that wireless communication device 108 transmits forwarded reservation signal 114 before the usefulness of forwarded reservation signal 114 expires. Optimally, wireless communication device 108 will transmit forwarded reservation signal 114 in the very next time-slot after the time-slot in which reservation signal 112 was transmitted. However, the next time-slot may not be available since it is likely that another wireless communication device will be using the next time-slot. Thus, in some examples, wireless communication device 108 will transmit forwarded reservation signal 114 in a next available time-slot. However, as shown in FIG. 3, there is another option besides waiting for the next available time-slot.

FIG. 3 is a diagram of an example in which a reservation signal is transmitted over a first portion of a time-slot and a forwarded reservation signal is transmitted over a second portion of the time-slot. For the example shown in FIG. 3, time-frequency domain 300 is provided where time, t, is represented on the horizontal axis and frequency, f, is represented on the vertical axis. Each box in the 10×10 grid of time-frequency domain 300 represents a time-slot that has both a corresponding time and frequency.

Each of the time-slots of time-frequency domain 300 may be allocated by the network to be utilized as resources for data transmissions, reservation channel transmissions, confirmation channel transmissions, or for reservation/confirmation channel transmissions. The reservation channel resource pool is comprised of the time-slots that are allocated for reservation channel transmissions.

In the example shown in FIG. 3, the network has utilized a pre-determined algorithm or formula to configure (e.g., allocate) 3 groups of time-slots, which are distributed non-periodically in time-frequency domain 300 and are filled in with cross-hatching, to be utilized in VANET 100 for reservation channel transmissions. Although a particular distribution and number of allocated time-slots has been shown in the example of FIG. 3, any other suitable distribution and number of allocated time-slots may be used, in other examples. In still other cases, the allocated time-slots for reservation channel transmissions could be uniformly distributed within time-frequency domain 300.

In the example shown in FIG. 3, a first group of time-slots 302 allocated for reservation channel transmissions is 3 F_(s) wide in the frequency domain, where F_(s) is the width of a single frequency band within time-frequency domain 300, and 1 time-slot long in the time domain. The first group of time-slots 302 is further divided into a first portion 304 (e.g., filled in with cross-hatching) and a second portion 306 (e.g., filled in with hatching), which are separated by a transmit/receive switching gap 308. In other examples, the first group of time-slots 302 may have any other suitable number and/or configuration of time-slots.

Base station 102 transmits, to one or more wireless communication devices 106, 108, 110, information regarding the non-periodic distribution of time-frequency resources (e.g., reservation channel resource pool) that are available to use for reservation channel transmissions. Upon receipt of the information regarding the reservation channel resource pool, the wireless communication devices select, from the reservation channel resource pool, time-frequency resources to use for reservation channel transmissions. In the example shown in FIG. 3, the first group of time-slots 302 are selected for reservation channel transmissions.

After selecting the first group of time-slots 302, wireless communication device 110 transmits reservation signal 112 over the first portion 304 of the selected first group of time-slots 302. After receiving reservation signal 112 in first portion 304 of first group of time-slots 302, wireless communication device 108 transmits, after transmit/receive switching gap 308, forwarded reservation signal 114 in second portion 306 of first group of time-slots 302.

In the example shown in FIG. 3, the time-slot has a transmit/receive switching gap 308 between the first portion 304 of the time-slot, in which the reservation channel transmissions 112 are made, and the second portion 306 of the time-slot, in which the forwarded reservation channel transmissions 114 are made. In some examples, the transmit/receive switching gap 308 is one or more orthogonal frequency-division multiplexing (OFDM) symbols in length.

In some examples, to differentiate between reservation signal 112 and forwarded reservation signal 114, wireless communication device 108 sets a flag in forwarded reservation signal 114 to indicate to wireless communication device 106 that reservation information contained in forwarded reservation signal 114 is being relayed. For example, the originating device of reservation signal 112 (e.g., wireless communication device 110) sets the flag=0. The first wireless communication device to broadcast forwarded reservation signal 114 (e.g., wireless communication device 108) increments the flag by 1. Subsequent re-broadcasts of the forwarded reservation signal 114 (e.g., at each hop) will continue to increment the flag by 1. Thus, the value of the flag included in each reservation signal or forwarded reservation signal will indicate the hop number to any wireless communication device that receives the reservation signal/forwarded reservation signal.

In other examples, the receiving wireless communication device 106 implicitly assumes that the broadcast in second portion 306 of a time-slot is the forwarded reservation signal 114. If multiple neighboring wireless communication devices are broadcasting the exact same forwarded reservation signal 114 in second portion 306 of the same time-slot, then the wireless communication devices that receive those duplicate transmissions of the same forwarded reservation signal 114 simply treat them as duplicate copies of the same forwarded reservation signal 114.

FIG. 4 is a flowchart of an example of a method in which a first wireless communication device receives, from a second wireless communication device, a reservation signal that identifies one or more time-slots that have been reserved by the second wireless communication device for data transmissions. The first wireless communication device transmits a forwarded reservation signal that identifies the one or more time-slots that have been reserved by the second wireless communication device. The method 400 begins at step 402 with receiving, at first wireless communication device 108, which is a node of VANET 100, from second wireless communication device 110, which is another node of VANET 100, a reservation signal 112 that identifies one or more time-slots that have been reserved by second wireless communication device 110 for data transmissions within VANET 100. At step 404, first wireless communication device 108 determines that first wireless communication device 108 is located near an edge of coverage area 111 associated with second wireless communication device 110. At step 406, first wireless communication device 108 transmits a forwarded reservation signal 114 that identifies one or more time-slots that have been reserved by second wireless communication device 110 for data transmissions within VANET 100. At step 408, first wireless communication device 108 transmits an updated forwarded reservation signal that identifies one or more remaining time-slots that were previously reserved by second wireless communication device 110 for data transmissions within VANET 100. In other examples, one or more of the steps of method 400 may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 4. In still further examples, additional steps may be added to method 400 that are not explicitly described in connection with the example shown in FIG. 4.

Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. 

1. A method comprising: receiving, at a first wireless communication device that is a node of a vehicle ad-hoc network (VANET) from a second wireless communication device that is another node of the VANET, a reservation signal that identifies one or more time-slots that have been reserved by the second wireless communication device for data transmissions within the VANET; and transmitting, from the first wireless communication device, a forwarded reservation signal that identifies the one or more time-slots that have been reserved by the second wireless communication device for data transmissions within the VANET, the forwarded reservation signal based, at least partially, on the reservation signal and containing information upon which one or more additional wireless communication devices may determine whether to transmit data within the one or more time-slots identified in the forwarded reservation signal.
 2. The method of claim 1, further comprising: determining, by the first wireless communication device, that the first wireless communication device is located near an edge of a coverage area associated with the second wireless communication device.
 3. The method of claim 2, wherein determining that the first wireless communication device is located near the edge of the coverage area associated with the second wireless communication device comprises: determining whether a received power value of the reservation signal is within a pre-defined threshold range value.
 4. The method of claim 2, wherein determining that the first wireless communication device is located near the edge of the coverage area associated with the second wireless communication device is based, at least partially, on location information associated with the second wireless communication device.
 5. The method of claim 4, wherein the location information is received in the reservation signal.
 6. The method of claim 1, wherein the reservation signal comprises one or more of the following: reservations for multiple time-slots, Global Positioning System (GPS) information, a zone identifier (zone ID), a number of time-slots reserved information, a cell identifier (cell ID), a group identifier (group ID), a frame-offset, and a subframe-offset.
 7. The method of claim 1, further comprising: transmitting, from the first wireless communication device, an updated forwarded reservation signal that identifies one or more remaining time-slots that were previously reserved by the second wireless communication device for data transmissions within the VANET, the updated forwarded reservation signal transmitted after at least one data transmission by the second wireless communication device.
 8. The method of claim 1, wherein transmitting the forwarded reservation signal comprises: transmitting the forwarded reservation signal in a next available time-slot.
 9. The method of claim 1, further comprising: receiving, at the first wireless communication device, the reservation signal in a first portion of a time-slot; and after a transmit/receive switching gap in the time-slot, transmitting, from the first wireless communication device, the forwarded reservation signal in a second portion of the time-slot.
 10. The method of claim 9, further comprising: setting, by the first wireless communication device, a flag in the forwarded reservation signal to indicate that reservation information contained in the forwarded reservation signal is being relayed.
 11. A first wireless communication device that is a node of a vehicle ad-hoc network (VANET), the first wireless communication device comprising: a receiver configured to receive, from a second wireless communication device that is another node of the VANET, a reservation signal that identifies one or more time-slots that have been reserved by the second wireless communication device for data transmissions within the VANET; and a transmitter configured to transmit a forwarded reservation signal that identifies the one or more time-slots that have been reserved by the second wireless communication device for data transmissions within the VANET, the forwarded reservation signal based, at least partially, on the reservation signal and containing information upon which one or more additional wireless communication devices may determine whether to transmit data within the one or more time-slots identified in the forwarded reservation signal.
 12. The first wireless communication device of claim 11, further comprising: a controller configured to determine that the first wireless communication device is located near an edge of a coverage area associated with the second wireless communication device.
 13. The first wireless communication device of claim 12, wherein the controller is further configured to determine whether a received power value of the reservation signal is within a pre-defined threshold range value.
 14. The first wireless communication device of claim 12, wherein the controller is further configured to determine that the first wireless communication device is located near the edge of the coverage area associated with the second wireless communication device based, at least partially, on location information associated with the second wireless communication device.
 15. The first wireless communication device of claim 14, wherein the location information is received in the reservation signal.
 16. The first wireless communication device of claim 11, wherein the reservation signal comprises one or more of the following: reservations for multiple time-slots, Global Positioning System (GPS) information, a zone identifier (zone ID), a number of time-slots reserved information, a cell identifier (cell ID), a group identifier (group ID), a frame-offset, and a subframe-offset.
 17. The first wireless communication device of claim 11, wherein the transmitter is further configured to transmit an updated forwarded reservation signal that identifies one or more remaining time-slots that were previously reserved by the second wireless communication device for data transmissions within the VANET, the updated forwarded reservation signal transmitted after at least one data transmission by the second wireless communication device.
 18. The first wireless communication device of claim 11, wherein the transmitter is further configured to transmit the forwarded reservation signal in a next available time-slot.
 19. The first wireless communication device of claim 11, wherein the receiver is further configured to receive the reservation signal in a first portion of a time-slot, and the transmitter is further configured to transmit, after a transmit/receive switching gap in the time-slot, the forwarded reservation signal in a second portion of the time-slot.
 20. The first wireless communication device of claim 19, further comprising: a controller configured to set a flag in the forwarded reservation signal to indicate that reservation information contained in the forwarded reservation signal is being relayed. 